Lysophospholipid is a collective name of phospholipids containing a single acyl group. Lysophospholipids have lower hydrophobicity than diacyl phospholipids, major components of the cell membrane, and they can be readily liberated from the cell membrane. It has been known that some lysophospholipids serve as signal molecules between cells or membranes and play important roles in the living organisms. In addition, it has been conventionally known that, when an inflammation such as tissue injury develops, phospholipids in a biomembrane are hydrolyzed to generate lysophospholipids (Patent Document 1). Lysophosphatidylserine (LysoPS), a type of lysophospholipid, has shown to be involved in acute inflammation by inducing degranulation of mast cells (Non-Patent Documents 1 and 2). The G protein-coupled receptors, GPR34, P2Y10, A630033H20Rik, and GPR174, have been identified as LysoPS receptors (Non-Patent Document 3); among these receptors, GPR34, P2Y10, and GPR174 are respectively referred to as LPS1, LPS2, and LPS3 (Non-Patent Document 4). It has been reported that LPS1 is involved in signal transduction for inducing or enhancing the degranulation reaction of mast cells, and it can be a target in the treatment of allergic diseases or chronic inflammation diseases (Patent Documents 1 and 2). Further, a specific lysophosphatidylserine derivative (lysophosphatidylthreonine) is known to dramatically accelerate degranulation reaction of mast cells (Patent Documents 3 and 4).
A screening method for compounds which are useful as autoimmune therapeutic agents as well as lysophosphatidylserine and its derivative that were found by the screening method have been reported (Patent Document 5). An autoimmune disease is a collective name of diseases in which the immune system, which is originally a protective system against foreign matters, overreacts and attacks a person's own normal cells and tissues such that symptoms appear. An autoimmune disease can be categorized into two types: a systemic autoimmune disease that affects the entire body, and an organ specific disease that affects only specific organs. In general, an autoimmune disease tends to be a chronic disease or an intractable disease, and some are identified in the list of Specified Disease Treatment Research Program by the Ministry of Health, Labour and Welfare. Numerous studies have been conducted on treatment methods of autoimmune diseases, and examples of those reported include a treatment method of chronic inflammation due to autoimmune disease, using a cytokine specific antibody involved in inflammation (Patent Document 6), and a treatment method of diseases by neutralizing the pathogenic autoantibody (Patent Document 7). However, much are left unanswered concerning the cause of autoimmune diseases, and establishment of effective therapeutic methods is awaited for many autoimmune diseases. A pharmaceutical agent for suppressing immunological systems or an anti-inflammatory agent for mitigating inflammation (a steroid or non-steroid agent) is used as a primary selection agent for autoimmune diseases.